Modulating clutch having passive torque throughout threshold

ABSTRACT

A modulating clutch for disposition and use in a motor vehicle drive train includes a disc pack clutch assembly and clutch actuator. The clutch actuator includes an assembly for generating compressive force which is applied to the clutch pack assembly and a preload member which partially engages the clutch pack to provide torque transfer up to a predetermined level without activation of the clutch actuator. Activation of the clutch actuator increases the torque transfer or throughput above the predetermined level. The differential of the present invention thus functions passively as a limited slip differential by allowing torques in excess of the predetermined torque level to slip each axle relative to the driveline input thereby provide a constant, minimum level torque coupling between the driveline and each axle. When the clutch actuator is energized, it may be utilized to control torque transfer at levels above the predetermined level between the input and output of the clutch mechanism. The modulating clutch of the present invention has application in vehicle differentials.

BACKGROUND OF THE INVENTION

The invention relates generally to modulating clutches for motor vehicledrivelines and more specifically to a clutch having a biasing orpreloading member which establishes a predetermined maximum torquethroughput without activation of the clutch operator.

Control systems and transfer cases having both electric and hydraulicmodulating clutches have found broad application in adaptive vehicledrive systems. Such systems generally monitor the speeds of the frontand rear drive shafts or compute such speeds by taking averages ofindividual readings of the two front and two rear wheels and, upondetermining a speed difference between the drive shaft speeds or averagespeeds of the wheels, energize the modulating clutch according to apredetermined program to drive the speed difference and thus wheel slipback to zero.

Typically, such modulating clutches are physically disposed in atransfer case adjacent and driven by the output of the vehicletransmission and operably disposed between the primary and secondarydrivelines. Systems exemplary of this configuration are disclosed inco-owned U.S. Pat. No. 5,407,024 granted Apr. 18, 1995 and U.S. Pat. No.5,485,894 granted Jan. 23, 1996.

Typically, when such modulating clutches are inactive (during periods ofequal drive shaft speed), they transfer either no torque from theprimary driveline to the secondary driveline or a residual or minimaltorque resulting merely from the internal drag of the clutch components.From a vehicle operational standpoint, such residual torque transfer isnegligible and thus irrelevant. While such configurations provideexceptionally accurate torque modulation and thus prop shaft speedcontrol when energized, they do have the drawback that until the clutchis activated or energized, substantially no torque transfer occurs.Stated somewhat differently, until or unless energy is expended toactuate the clutch, no torque transfer occurs. This is, of course, truewhether the modulating clutch is disposed in a transfer case or adifferential.

Given this operational rule, maintaining even a minimal, standby torquewhich maintains the secondary driveline components in a stagedcondition, that is, with all slack taken up, ready to transfer drivetorque, can be accomplished only by the constant consumption of energy.In a clutch having an electromagnetic operator, this constantenergization of the electromagnetic coil not only constantly consumeselectrical energy but can also result in objectionable magnetization ofdriveline components and other proximate ferrous vehicle componentswhich, while not deleterious, is preferably avoided.

From the foregoing, it is apparent that improvements relating to the artof modulating clutches specifically intended for use in the drivelinesof motor vehicles addressing these drawbacks would be desirable.

SUMMARY OF THE INVENTION

A modulating clutch for disposition and use in a motor vehicle drivetrain includes a disc pack clutch assembly and clutch actuator. Theclutch actuator includes an assembly for generating compressive forcewhich is applied to the clutch pack assembly and a preload member whichpartially engages the clutch pack to provide torque transfer up to apredetermined level without activation of the clutch actuator.Activation of the clutch actuator increases the torque transfer orthroughput above the predetermined level.

The modulating clutch of the present invention has application invehicle differentials. The differential of the present invention thus,first of all, functions passively as a limited slip differential byallowing torques in excess of the predetermined torque level to slipeach axle relative to the driveline input thereby provide a constant,maximum torque level coupling between the driveline and each axle.Second of all, when the clutch actuator is energized, it may be utilizedto control torque transfer at levels above the predetermined levelbetween the input and output of the clutch mechanism. Lastly, theclutches may be commonly or individually controlled to achieve uniformleft-right or distinct left-right torque distribution.

The preloading or biasing member provides a passive maximum torquethroughput which can then be increased by the activation of the clutchactuator. This torque throughput threshold is additive to the torquetransfer capability of clutch actuator as the limiting factor of torquethroughputs through such a modulating clutch is the amount ofcompressive force generated by the clutch operator, not the torquethroughput capability of the clutch pack itself. Thus through the use ofa biasing or preloading member, the total torque throughput capabilityof such a clutch can be increased while maintaining the same packagesize, service life and operating parameters.

Thus it is the object of the present invention to provide a modulatingclutch having an internal biasing or preloading member which providestorque throughput up to a predetermined threshold.

It is a further object of the present invention to provide a modulatingclutch having a biasing or preloading member which couples the input andoutput up to a maximum torque level without consuming operating energy.

It is a still further object of the present invention to provide amodulating disc pack clutch having a predetermined torque throughputwhich can be increased by the activation of the clutch operator.

It is a still further object of the present invention to provide amodulating clutch which can provide increased torque throughput relativeto pre-existing package size and service life constraints.

It is a still further object of the present invention to provide amodulating clutch having a biasing or preloading member which increasestotal torque throughput capability.

Further objects and advantages of the present invention will becomeapparent by reference to the following description of the preferredembodiment and appended drawings wherein like reference numbers refer tothe same element, component or feature.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagrammatic view of a vehicle drive system for a four-wheelvehicle incorporating the dual clutch secondary driveline differentialof the present invention;

FIG. 2 is a full, sectional view of a dual clutch differential accordingto the present invention;

FIG. 3 is an enlarged, sectional view of a portion of a dual clutchdifferential according to the present invention; and

FIG. 4 is a flat pattern development of the ball ramp operators of theclutch according to the present invention taken along line 4--4 of FIG.3.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring now to FIG. 1, an adaptive four-wheel vehicle drive train isdiagrammatically illustrated and designated by the reference numeral 10.The four-wheel vehicle drive train 10 includes a prime mover 12 which iscoupled to and directly drives a transaxle 14. The output of thetransaxle 14 drives a beveled or spiral beveled gear set 16 whichprovides motive power to a primary or front driveline 18 comprising afront or primary propshaft 20, a front or primary differential 22, apair of live front axles 22 and respective pair of front or primary tireand wheel assemblies 26. The beveled or spiral beveled gear set 16 alsoprovides motive power to a secondary or rear driveline 28 comprising asecondary propshaft 30 having appropriate universal joints 32, a rear orsecondary differential 34, a pair of live secondary or rear axles 36 anda respective pair of secondary or rear tire and wheel assemblies 38.

The foregoing description relates to a vehicle wherein the primarydriveline 18 is disposed at the front of the vehicle and,correspondingly, the secondary driveline 28 is disposed at the rear ofthe vehicle, such a vehicle commonly referred to as a front wheel drivevehicle. The designations "primary" and "secondary" herein refer todrivelines providing drive torque at all times and drivelines providingsupplemental or intermittent torque, respectively. These designations(primary and secondary) are utilized rather than front driveline andrear driveline inasmuch as the invention herein disclosed and claimedmay be readily utilized with vehicles wherein the primary driveline 18is disposed at the rear of the vehicle and the secondary driveline 28and components within the secondary differential 34 are disposed at thefront of the vehicle. Thus, the illustration in FIG. 1, wherein theprimary driveline 18 is disposed at the front of the vehicle should beunderstood to be illustrative rather than limiting and that thecomponents and arrangement of components illustrated is equally suitableand usable with a primary rear wheel drive vehicle.

Referring now to FIGS. 1 and 2, the secondary differential 34 includesan input shaft 40 supported for rotation on suitable roller bearingassemblies 42 within a center housing 44. At each end of the centerhousing 44 is a bell housing 46 which is secured to the center housing44 by a plurality of fasteners 48, two of which are illustrated in FIG.2. Appropriately disposed oil seals 52 provide an appropriatefluid-tight seal between the input shaft 40 and the housing 44. A tonewheel 54 is also secured for rotation to the input shaft 40 and rotatestherewith. A sensor 56 such as a variable reluctance or Hall effectsensor extends through the center housing 44 and senses rotation of thetone wheel 54. The input shaft 40 may also include male splines or othersimilar features which facilitate coupling to a universal joint 32 orother shaft or stub shaft which drives the input shaft 40.

The input shaft 40 terminates in a bevel gear 62 having gear teeth 64which mate with complementarily configured gear teeth 66 on a ring gear68 secured to a flange 72 on a centrally disposed tubular drive member74 by suitable fasteners 76. The tubular drive member 74 is supported bya pair of anti-friction bearings such as the ball bearing assemblies 78which are seated within the center housing 44 on an annular spacer 82disposed within the center housing 44. At each end of the tubular drivemember 74 are sets of male splines or gear teeth 84. Within each of thepair of bell housings 46 is a respective one of a pair of modulatingclutch assemblies 90A and 90B. But for the opposed, mirror-imagearrangement of the two modulating clutch assemblies 90A and 90B, thecomponents of the two clutch assemblies 90A and 90B described below theyare identical and thus only the modulating clutch assembly 90B disposedon the right of FIG. 2 and in FIG. 3 will be fully described, it beingunderstood that the left modulating clutch assembly 90A is in allsignificant respects identical to the right modulating clutch 90A.

Each of the modulating clutch assemblies 90A and 90B include a clutchend bell 92. The clutch end bells 92 are identical but disposed in amirror image relationship on opposite ends of the tubular drive member74. Each of the clutch end bells 92 includes a plurality of femalesplines or gear teeth 94 formed in the end wall which are complementaryto the male splines or gear teeth 84 on the tubular drive member 74. Theinterior, circumferential surface of the bell housing 92 defines aplurality of axially extending female splines 96 which are engaged byand rotationally drive complementary male splines 98 disposed on a firstplurality of clutch plates 100. The first plurality of clutch discs orplates 100 include suitable frictional material and surfaces and areinterleaved with a second, smaller diameter plurality of clutch discs orplates 102 also including suitable frictional material and surfaces andhaving female splines 104 which engage and rotationally drivecomplementary male splines 106 disposed upon a clutch collar 108. Theclutch collar 108 in turn includes female splines or gear teeth 110which mate with complementarily configured male splines or gear teeth112 disposed on the output shaft 114B.

The disc pack clutch assembly 90B also includes a circular apply plate116 which includes internal splines or gear teeth 118 which mate withthe male splines 106 on the clutch collar 108. The apply plate 116 thusrotates with the second plurality of clutch plates 102 and may moveaxially relative thereto. The apply plate 116 includes a shoulder 122which positions and receives a Belleville spring 124. The Bellevillespring provides a compressive preload or bias to the first and secondpluralities of clutch plates 100 and 102 such that a nominal maximumtorque of 150 pounds-feet may be transmitted through the clutches 90Aand 90B before slip occurs. The maximum torque threshold through eachclutch assembly 90A and 90B may be adjusted up or down by 50% or more,e.g., 75 pounds-feet to 225 pounds-feet by, for example, adjustment ofthe compressive force provided by the Belleville spring 124, to suittypical automotive, 4 WD vehicle and SUV applications.

In a typically sized clutch pack, the nominal torque transfer achievableby actuator compression of the disc clutch pack is on the order of 350pounds-feet. The torques are additive and thus the total torque of thedisc pack clutch assembly 90A and 90B equipped with the Bellevillespring 124 will be on the order of 500 pounds-feet.

The Belleville spring 124 is disposed between the apply plate 116 and anarmature 126. The armature 126 include male splines or gear teeth 128about its periphery which are complementary to and engage the femalesplines 96 on the interior of the end bell 92. Thus, the armature 126rotates with the end bell 92 and the first plurality of clutch plates100. The armature 126 is disposed adjacent a U-shaped circular coilhousing 132. The coil housing 132 generally surrounds a stationaryelectromagnetic coil 134 which is secured to the housing end bell 46 bya plurality of threaded studs and fasteners 136. Electrical energy maybe provided to the electromagnetic coil 134 through a conductor 138.

Coupled to the coil housing 132 by any suitable means such as weldments,interengaging splines or an interference fit is a first circular member140. The first circular member 140 defines a loose, freely rotating fitabout the output shaft 114B and thus the first circular member 140 andthe coil housing 132 are free to rotate about both the output shaft 114Band the electromagnetic coil 134. The first circular member 140 includesa plurality of ramp-like recesses 142 arranged in a circular patternabout the axis of the output shaft 114B. The recesses 142 represent anoblique section of a helical torus. Disposed within each of the recesses142 is a load transferring ball 144 or similar load transferring memberwhich rolls along the ramps defined by the oblique surfaces of therecesses 142. A second circular member 146 is disposed in opposedrelationship with the first circular member 140 and includes a likeplurality of complementarily sized and arranged recesses 148. The loadtransferring balls 144 are thus received and trapped within the pairs ofopposing recesses 142 and 148, the ends of the recesses being curved andmuch steeper in slope than the interior regions of the recesses 142 and148 such that the load transferring balls 144 are effectively trapped inthe regions defined thereby.

It will be appreciated that the recesses 142 and 148 and the loadtransferring balls 144 may be replaced with other analogous mechanicalelements which cause axial displacement of the circular members 140 and146 in response to relative rotation therebetween. For example, taperedrollers disposed in complementarily configured conical helices may beutilized.

An important design consideration of the recesses 142 and 148 and theload transferring balls 144 is that the geometry of their design and thedesign of the Belleville spring 124 and the clearances in the clutchassembly overall ensure that the clutch assemblies 90A and 90B are notself-locking. The electromagnetic clutch assemblies 90A and 90B must notself-engage but rather must be capable of modulating clamping of theclutch plates 100 and 102 and torque transfer in direct, proportionalresponse to the input to the electromagnetic coil 134.

The second circular member 146 includes a plurality of female splines orgear teeth 152 which are complementary to and engage the male splines orgear teeth 112 on the output shaft 114. The axial position of the firstcircular member 140 is established by a thrust bearing 156 which isdisposed adjacent a ball bearing assembly 158. Each of the output shafts114A and 114B include a tone wheel 162A and 162B. Disposed in adjacent,sensing relationship with each of the tone wheels 162A and 162B is avariable reluctance or Hall effect sensor 164A and 164B. The sensors164A and 164B provide signals which may be utilized by suitableelectronic equipment to compute the speed of the left and right outputshafts 114A and 114B, respectively. Oil seals 166 are also disposedbetween the output shafts 114A and 114B and the housing end bells 46.Finally, output flanges 168 may be secured by suitable splines or otherinterconnecting means to the output shafts 114 to facilitate coupling ofthe output shafts 114 to associated components in the rear axles 36 ofthe secondary driveline 28.

In order to provide appropriate cooling for the components of thesecondary driveline differential 34 and specifically of the modulatingclutch assemblies 90A and 90B, the interior portion of the housing 44forms a sump within which a lubricating and cooling fluid may bedisposed. A pair of scavengers or scoops 172 having a mouth open towardthe forward direction of rotation of the tubular drive member 74 extendradially therefrom. As the tubular drive member 74 rotates, the scoops172 collect and drive lubricating and cooling fluid inwardly to acentrally dispose, hollow chamber 174 in the tubular drive member 74.Fluid then travels through axial passageways 176 in the output shafts114 and thence through radial passageways 178 and into the region of thedifferential 34 occupied by the modulating clutch assemblies 90A and90B. Heat generated in the modulated clutch assemblies 90A and 90B isthus transferred to the circulating lubricating and coolant fluid anddispersed throughout the secondary differential 34.

Operation of the secondary driveline differential 34 and, specficially,the modulating clutch assemblies 90A and 90B, may comprehend commonoperation, i.e., both clutch assemblies 90A and 90B driven by the samecontrol signal or individual operation, for example, wherein individualcontrol signals control torque delivery to each individual secondarytire and wheel assembly 38 to compensate for or correct left-right speeddifferences. Furthermore, the passive torque throughput threshold of thedifferential 34 provides operation comparable to that of a limited slipdifferential without energizing the electromagnetic coils 134.Energization of such coils 134 then allows the control in delivery oftorque to both or each individual secondary wheel 38 at higher levelsdetermined by the degree of clutch activation.

The foregoing disclosure is the best mode devised by the inventor forpracticing this invention. It is apparent, however, that apparatus andmethods incorporating modifications and variations will be obvious toone skilled in the art of vehicle clutches and drivelines. Inasmuch asthe foregoing disclosure is intended to enable one skilled in thepertinent art to practice the instant invention, it should not beconstrued to be limited thereby but should be construed to include suchaforementioned obvious variations and be limited only by the spirit andscope of the following claims.

I claim:
 1. A clutch for use in a differential or transfer case of afour-wheel drive vehicle comprising, in combination,an input member, anoutput member, a modulating clutch assembly disposed between said inputmember and said output member, said modulating clutch having a firstplurality of clutch discs disposed for rotation with said input member,a second plurality of clutch discs interleaved with said first pluralityof clutch discs and disposed for rotation with said output member, aclutch operator for adjustably compressing said first and said secondpluralities of clutch discs, said clutch operator having an assemblyincluding a pair of opposed members defining a plurality of rampedrecesses, a like plurality of load transferring members disposed in arespective one of said recesses and an electromagnetic coil forretarding rotation of one of said opposed members, and means forcompressing said first and said second pluralities of clutch discs toprovide a predetermined level of frictional coupling between said inputmember and said output member.
 2. The clutch of claim 1 wherein saidmeans for compressing is a passive, non-adjustable spring.
 3. The clutchof claim 1 wherein said means for compressing is a Belleville spring. 4.The clutch of claim 1 wherein said frictional coupling is between 100and 200 pounds-feet.
 5. The clutch of claim 1 further including a secondoutput member and second modulating clutch driven by said input memberand driving said second output member.
 6. A differential for use in afour-wheel drive vehicle comprising, in combination,an input member, apair of output members, and a pair of modulating clutch assemblies, eachof said modulating clutches having a first plurality of clutch discsdisposed for rotation with said input member, a second plurality ofclutch discs interleaved with said first plurality of clutch discs anddisposed for rotation with said output member, a clutch operator forcompressing said first and said second pluralities of clutch discs, saidclutch operator having an assembly including a pair of opposed membersdefining a plurality of ramped recesses, and a like plurality of loadtransferring members disposed in a respective one of said recesses andan electromagnetic coil for retarding rotation of one or aid opposedmembers, and means for operably associated with said pluralities ofclutch discs providing a predetermined level of frictional couplingbetween said input member and said output member.
 7. The differential ofclaim 6 wherein said means for providing is a Belleville spring.
 8. Thedifferential of claim 6 wherein said frictional coupling is between 75pounds-feet and 225 pounds-feet.
 9. The differential of claim 6 whereinsaid clutch operator includes an electromagnetic coil.
 10. Thedifferential of claim 6 wherein said means for providing is anon-adjustable spring.
 11. A differential for use in an adaptivefour-wheel drive vehicle comprising, in combination,an input shaft, adrive member disposed perpendicularly to said input shaft, a gear setfor transferring rotational energy from said input shaft to said drivemember, a pair of output shafts aligned with said drive member and apair of modulating clutch assemblies, one of said pair of modulatingclutch assemblies disposed between and selectively coupling each of saidoutput shafts with said drive member, each of said modulating clutchesincluding a disc pack and first operator for adjustably compressing saiddisc pack, said first operator having an assembly including a pair ofopposed members defining a plurality of ramped recesses, a likeplurality of load transferring members disposed in a respective one ofaid recesses and an electromagnetic coil for retarding rotation of oneof said opposed members, and a second operator for providing apredetermined level of frictional coupling through said disc pack. 12.The differential of claim 9 wherein said second operator is anon-adjustable spring.
 13. The differential of claim 9 wherein saidsecond operator is a Belleville spring.
 14. The differential of claim 9wherein said frictional coupling is between 75 pounds-feet and 225pounds-feet.
 15. The differential of claim 9 further including a tonewheel disposed for rotation with each of said output shafts and sensingmeans disposed adjacent each of said tone wheels.
 16. The differentialof claim 9 further including fluid scavengers disposed upon said drivemember.